A SURVEY OF MOBILE DATA NETWORKS APOSTOLIS K. SALKINTZIS THE UNIVERSITY OF BRITISH COLUMBIA ABSTRACT The proliferation and development of cellular voice systems over the past several years has exposed the capabilities and the effectiveness of wireless communications and, thus, has paved the way for wide-area wireless data applications as well. The demand for such applications is currently experiencing a significant increase and, therefore, there is a strong call for advanced and efficient mobile data technologies. This article deals with these mobile data technologies and aims to exhibit their potential. It provides a thorough survey of the most important mobile packet data services and technologies, including MOBITEX, CDPD, ARDIS, and the emerging GPRS. For each technology, the article outlines its main technical characteristics, discusses its architectural aspects, and explains the medium access protocol, the services provided, and the mobile routing scheme. istorically, wireless data communications was princi- and have access to external data, wireless data technology pally the domain of large companies with special- plays a significant part because it can offer ubiquitous con- ized needs; for example, large organizations that nectivity, that is, connectivity at any place, any time. For this needed to stay in touch with their mobile sales reason, wireless data technology can be of real value to the Hforce, or delivery services that needed to keep track of their business world since computer users become more productive vehicles and packages. However, this situation is steadily when they exploit the benefits of connectivity. The explosive changing and wireless data communications is becoming as growth of local area network (LAN) installations over the commonplace as its wired counterpart. past several years is ample evidence of the importance placed The need for wireless data communications arises partially on connectivity by the business world. because of the need for mobile comput- ing and partially because of the need for specialized applications, such as comput- erized dispatch services and mobile fleet management. Mobile computing, which aims to migrate the computing world onto a mobile environment, is affected primari- ly by two components: portability and connectivity. Portability, i.e., the ability to untether computers from the conven- tional desktop environment, is getting increasingly feasible because with the continuous improvement in integration, miniaturization, and battery technology, the differences in performance and cost between desktop and portable computers is shrinking. Therefore, the processing power of desktop computing is becoming available to portable environments and this is highly desirable as far as produc- tivity is concerned. Regarding the connectivity, i.e., the ability to connect to external resources ■ FIGURE 1. Categories of wireless data networks. 2 IEEE Communications Surveys • http://www.comsoc.org/pubs/surveys • Third Quarter 1999, vol. 2 no. 3 ■ FIGURE 2. Schematic illustration of mobile data applications. Usually, portability and connectivity are at odds: the kb/s, and HSCSD is designed to offer up to 56 kb/s over con- more portability increases, the more difficult it becomes to ventional voice channels. connect to external resources. However, wireless data tech- On the other hand, local-area wireless data networks, nology provides the means to effectively combine both capa- which are typically employed as private systems in businesses, bilities and, therefore, it is an essential technology for conference rooms, university campuses, and so on, provide mobile computing. wireless data service in a small geographical area and, for this Fig. 1 presents the various wireless data technologies, reason, they do not experience the same rough physical layer which are essentially divided into two categories according to constraints of their wide-area counterparts. Therefore, they their mobility characteristics. For wide-area mobility there are capable of supporting high-speed wireless data transmis- are mainly two available technologies: data transmission over sion, on the order of a few Mb/s. For local-area mobility cellular networks, whether analog or digital, and data trans- there are mainly two alternatives: data transmission over mission over mobile data networks. As shown in Fig. 1, the cordless systems (e.g., over CT-2 or DECT) and over wireless main difference between these two technologies is the data local area networks (LANs). As indicated in Fig. 1, cordless transport mode. Cellular networks, being primarily voice ori- systems provide circuit-switching transport service, whereas ented, utilize circuit switching technology1 and, therefore, are wireless LANs provide packet-switching transport service. optimized to isochronous data traffic conditions, whereas From the previous discussion it becomes apparent that mobile data networks employ packet switching technology there are two wireless packet data technologies: mobile data and are ideal for asynchronous data traffic transmission. Cur- networks, which support wide-area, low-speed service, and rently, due to physical layer constraints, wide-area networks wireless LANs, which support local-area, high-speed service. typically feature low-speed wireless data transmission, on the These technologies use packet switching to transport data order of 9600 b/s. However, with the emerging new protocols, rather than circuit switching, which is typically used in cellu- much higher data transmission speed is supported. For exam- lar or cordless networks. ple, GPRS will support data transmission rates up to 115 The rest of this article is devoted to mobile data technolo- gy. The next section provides an outline of the most impor- tant mobile data applications and discusses several service 1 Some digital cellular networks (such as GSM) will utilize packet data providers that operate mobile data networks worldwide. The service in the near future. following four sections discuss in detail the MOBITEX, IEEE Communications Surveys • http://www.comsoc.org/pubs/surveys • Third Quarter 1999, vol. 2 no. 3 3 Application area Specific applications Mobile office •Remote office access or database access CDPD, GPRS, and mobile data •File transfer technologies/services, respectively, addressing •Administrative control •Two-way communications the most significant issues of each technology. •Internet browsing via the World Wide Web The final section summarizes our main conclu- s i o n s . Financial and retail •Transactions such as electronic cash or fund transfers communications which, generally, do not have very high communication requirements MOBILE DATA APPLICAT IONS •Card authorization at points of sale in retail outlets Circuit-switching and packet-switching can Remote control and •Traffic and transport informatics make a great difference in terms of transmis- monitoring •Traffic light monitoring and traffic movement sion cost, throughput, and service quality. measurements There are some applications that are best suit- •Route guidance systems •Variable message signs on the roadside to inform drivers ed to the circuit-switching model, while others of forthcoming events or problems on the road ahead are best suited to the packet-switching model. •Train control systems In general, packet switching is more efficient •Vehicle fleet management and consequently less costly for “bursty” appli- •Gas, water, and electricity metering systems cations that transmit small quantities of data at •Remote monitoring and controlling of vending machines every transmission. On the other hand, circuit •General telemetry systems switching is more efficient for large file trans- missions. Alarm signaling From the user’s perspective, wireless packet data networks (which employ packet-switching) ■ Wireless packet data applications. Table 1. offer an alternative that usually guarantees both cheaper and improved services in a vast Operator URL Service Equipment Encoding Coverage Roaming (population) Belgium/Ram http://www.ram.be Ram Mobile Data Handheld terminals; Mobitex 97% The Nether- Mobile Data radio modems 8 kbit/s lands, U.K. Finland/Telecom http://www.tele.fi Mobitex Network Vehicle-mounted Mobitex 95% No Finland terminals; radio 1.2 kbit/s modems Germany/ http://www.t-mobil.de Modacom Handheld terminals; Datatek 6000 95% No Detemobil radio modems 9.6 kbit/s Netherlands/Ram http://www.ram.nl Ram Mobile Data Handheld terminals; Mobitex 98% Belgium, U.K. Mobile Data radio modems 8 kbit/s Sweden/Telia http://www.mobitex. Mobitex Vehicle-mounted Mobitex 98% No Mobile telia.com terminals; radio 1.2 kbit/s modems U.K./Cognito http://www.cognito. Cognito Mobile Data Cognito Messager Cognito 87% No co.uk Solutions terminal; Cognito encoding radio modem 9.6 kbit/s U.K./Paknet http://www.vodafone. Paknet Handheld terminals; Paknet encoding 95% No co.uk radio modems 8 kbit/s U.K./Ram Mobile http://www.ram.co.uk Ram Mobile Data Handheld terminals; Mobitex 8 kbit/s 89% Belgium, The Data radio modems Netherlands U.K./Securicor http://www.securicor. Datatrak Network Vehicle-mounted Securicor Not No Datatrak co.uk terminal; radio encoding disclosed modems 10 kbit/s USA/Bellsouth http://www.bellsouthwd. Bellsouth Wireless Handheld terminals; Mobitex 8 kbit/s 93% of USA com Data two-way pagers; metro areas radio modems Canada/Rogers http://www.cantel.com Rogers Cantel Handheld terminals; Mobitex 8 kbit/s Main Canada Cantel Wireless Data two-way pagers; metro cities radio modems USA/American